In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first product, Cardinal 640, has a 640×512 (VGA) format at 15μm pitch, and more than two thousand units have already been delivered to customers. Recently we have also introduced Cardinal 1280 which is an SXGA array with 10μm pitch aimed for long-range high end platforms . One of the big challenges facing the SWIR technology is its proliferation to widespread low cost and low SWaP applications, specifically Low Light Level (LLL) and Image Intensifier (II) replacements. In order to achieve this goal we have invested and combined efforts in several design and development directions: 1. Optimization of the InGaAs pixel array, reducing the dark current below 2fA at 20° C in order to save TEC cooling power under harsh light and environmental conditions. 2. Design of a new "Low Noise" ROIC targeting 15e noise floor and improved active imaging capabilities 3. Design of compact, low SWaP and low cost packages. In this context we have developed 2 types of packages: a non-hermetic package with thermo-electric cooler (TEC) and a hermetic TEC-Less ceramic package. 4. Development of efficient TEC-Less algorithms for optimal imaging at both day-light and low light level conditions. The result of these combined efforts is a compact low SWaP detector that provides equivalent performance to Gen III image intensifier under starlight conditions. In this paper we will present results from lab and field experiments that will support this claim.
In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first
product, Cardinal 640, has a 640x512 (VGA) format at 15μm pitch, and more than a thousand units have already
We now present Cardinal 1280, having the smallest pitch available today (10μm), with a 1280x1024 (SXGA)
format. Cardinal 1280 addresses both long-range daylight imaging, and passive or active imaging in Low Light
Level (LLL) conditions.
The Readout Integrated Circuit supports snapshot imaging at 13 bit resolution with a frame rate of 160Hz at full
format, or a frame rate of 640Hz with 2x2 binning. It also has a Low Noise Imaging (LNIM) mode with 35ereadout
noise with internal Correlated Double Sampling (CDS). An asynchronous Laser Pulse Detection (ALPD)
mode is implemented with 2x2 binning in parallel to SWIR imaging (with 10 μm resolution). The new 10 μm
pixel is sensitive down to the visible (VIS) spectrum, with a typical dark current of ~ 0.5fA at 280K, and a
quantum efficiency >80% at 1550nm.
The Focal Plane Array is integrated into a ruggedized, high vacuum integrity, metallic package, with a Thermo-
Electric Cooler (TEC) for optimized performance, and a high grade Sapphire window. In this paper we will
present the architecture and preliminary measurement results.
Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR atmospheric window (3.4 - 4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4 - 4.9 μm), and thus is especially useful for mid and long range applications. The detector has an InAsSb active layer and is based on the new "XBn" device concept, which eliminates Generation-Recombination dark current and enables operation at temperatures of 150K or higher, while maintaining excellent image quality. Such high operating temperatures reduce the cooling requirements of Focal Plane Array (FPA) detectors dramatically, and allow the use of a smaller closed-cycle Stirling cooler. As a result, the complete Integrated Detector Cooler Assembly (IDCA) has about 60% lower power consumption and a much longer lifetime compared with IDCAs based on standard InSb detectors and coolers operating at 77K. In this work we present a new large format IDCA designed for 150K operation. The 15 μm pitch 1280×1024 FPA is based on SCD's XBn technology and digital Hercules ROIC. The FPA is housed in a robust Dewar and is integrated with Ricor's K508N Stirling cryo-cooler. The IDCA has a weight of ~750 gram and its power consumption is ~ 5.5 W at a frame rate of 100Hz. The Mean Time to Failure (MTTF) of the IDCA is more than 20,000 hours, greatly facilitating 24/7 operation.
Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD,
which operates in the blue part of the MWIR window of the atmosphere (3.4-4.2 μm). This window is generally more
transparent than the red part of the MWIR window (4.4-4.9 μm), especially for mid and long range applications. The
detector has an InAsSb active layer, and is based on the new "XBn" device concept. We have analyzed various electrooptical
systems at different atmospheric temperatures, based on XBn-InAsSb operating at 150K and epi-InSb at 95K,
respectively, and find that the typical recognition ranges of both detector technologies are similar. Therefore, for very
many applications there is no disadvantage to using XBn-InAsSb instead of InSb. On the other hand XBn technology
confers many advantages, particularly in low Size, Weight and Power (SWaP) and in the high reliability of the cooler
and Integrated Detector Cooler Assembly (IDCA). In this work we present a new IDCA, designed for 150K operation.
The 15 μm pitch 640×512 digital FPA is housed in a robust, light-weight, miniaturised Dewar, attached to Ricor's
K562S Stirling cycle cooler. The complete IDCA has a diameter of 28 mm, length of 80 mm and weight of < 300 gm.
The total IDCA power consumption is ~ 3W at a 60Hz frame rate, including an external miniature proximity card
attached to the outside of the Dewar. We describe some of the key performance parameters of the new detector,
including its NETD, RNU and operability, pixel cross-talk, and early stage yield results from our production line.
In MWIR photodiodes made from InSb, InAs or their alloy InAs1-xSbx, the dark current is generally limited by
Generation-Recombination (G-R) processes. In order to reach a background limited operating temperature higher than
~80 K, steps must be taken to suppress this G-R current. At SCD we have adopted two main strategies. The first is to
reduce the concentration of G-R centres, by changing from an implanted InSb diode junction to a higher quality one
grown by Molecular Beam Epitaxy (MBE). Our epi-InSb diodes have a background limited performance (BLIP)
temperature of ~105 K at F/4, in 15 to 30 μm pitch Focal Plane Arrays (FPAs). This operation temperature increase
delivers a typical saving in cooling power of ~20%. In order to achieve even higher operating temperatures, we have
developed a new XB<sub>n</sub>n bariode technology, in which the bulk G-R current is totally suppressed. This technology
includes nB<sub>n</sub>n and pB<sub>n</sub>n devices, as well as more complex structures. In all cases, the basic unit is an n-type AlSb<sub>1-y</sub>As<sub>y</sub> /
InAs<sub>1-x</sub>Sb<sub>x</sub> barrier layer / photon-absorbing layer structure. These FPAs, with 15 to 30 μm pitch and a cut-off
wavelength of ~ 4.1 μm, exhibit a BLIP temperature of ~ 175K at F/3. The cooling power requirement is reduced by
~60% compared with conventional 77K operation. The operation of both our diode and bariode detectors at high
temperatures results in an improved range of solutions for various applications, especially where Size, Weight, and
Power (SWaP) are critical. Advantages include faster cool-down time and mission readiness, longer mission times, and
higher cooler reliability, as well as very low dark current and an enhanced Signal to Noise Ratio (SNR) at lower
operating temperatures. This paper discusses the system level performance for cut-off wavelengths appropriate to the
sensing materials in each detector type. Details of the radiometric parameters of each detector type are then presented in
Short wavelength Infra Red (SWIR) imaging has gained considerable interest in recent years. The main applications
among others are: active imaging and LADAR, enhanced vision systems, low light level imaging and security
In this paper we will describe SCD's considerable efforts in this spectral region, addressing several platforms:
1. Extension of the mature InSb MWIR product line operating at 80K (cut-off wavelength of 5.4μm).
2. Extension of our new XB<sub>n</sub><i>n</i> InAsSb "bariode" technology operating at 150K (cut-off of 4.1μm).
3. Development of InGaAs detectors for room temperature operation (cut-off of 1.7μm)
4. Development of a SNIR ROIC with a low noise imaging mode and unique laser-pulse detection modes.
In the first section we will present our latest achievements for the cooled detectors where the SWIR region is combined
with MWIR response. Preliminary results for the NIR-VIS region are presented where advanced substrate removal
techniques are implemented on flip-chip hybridized focal plane arrays.
In the second part we will demonstrate our VGA, 15μm pitch, InGaAs arrays with dark current density below 1.5nA/cm<sup>2</sup>
at 280K. The InGaAs array is hybridized to the SNIR ROIC, thus offering the capability of low SWaP systems with
laser-pulse detection modes.
A bariode is a new type of "diode-like" semiconductor photonic device, in which the transport of majority carriers is
blocked by a barrier in the depletion layer, while minority carriers, created thermally or by the absorption of light, are
allowed to pass freely across the device. In an n-type bariode, also known as an XB<sub>n</sub>n structure, both the active photon
absorbing layer and the barrier layer are doped with electron donors, while in a p-type bariode, or XB<sub>p</sub>p structure, they
are both doped with electron acceptors. An important advantage of bariode devices is that their dark current is
essentially diffusion limited, so that high detector operating temperatures can be achieved. In this paper we report on
MWIR n-type bariode detectors with an InAsSb active layer and an AlSbAs barrier layer, grown on either GaSb or
GaAs substrates. For both substrate types, the bariodes exhibit a bandgap wavelength of ~ 4.1 μm and operate with
Background Limited Performance (BLIP) up to at least 160K at F/3. Different members of the XBnn device family are
investigated, in which the contact layer material, "X", is changed between n-InAsSb and p-GaSb. In all cases, the
electro-optical properties of the devices are similar, showing clearly the generic nature of the bariode device
architecture. Focal Plane Array detectors have been made with a pitch of 15 or 30μm. We present radiometric
performance data and images from our Blue Fairy (320×256) and Pelican (640×512) detectors, operating at
temperatures up to 180K. We demonstrate for both GaSb and GaAs substrates that detector performance can be
achieved which is close to "Rule 07", the benchmark for high quality, diffusion limited, Mercury Cadmium Telluride
We demonstrate the suppression of the bulk generation-recombination current in nBn devices based on an InAsSb active layer (AL) and a AlSbAs barrier layer (BL). This leads to much lower dark currents than in conventional InAsSb photodiodes operating at the same temperature. When the BL is p-type, very high doping must be used in the AL (nBpn+). This results in a significant shortening of the device cutoff wavelength due to the Moss-Burstein effect. For an n-type BL, low AL doping can be used (nBnn), yielding a cutoff wavelength of ∼4.1 μm and a dark current close to ∼3 × 10−7 A/cm2 at 150 K. Such a device with a 4-μm-thick AL will exhibit a quantum efficiency (QE) of 70% and background-limited performance operation up to 160 K at f/3. We have made nBnn focal plane array detectors (FPAs) with a 320 × 256 format and a 1.3-μm-thick AL. These FPAs have a 35% QE and a noise equivalent temperature difference of 16 mK at 150 K and f/3. The high performance of our nBnn detectors is closely related to the high quality of the molecular beam epitaxy grown InAsSb AL material. On the basis of the temperature dependence of the diffusion limited dark current, we estimate a minority carrier lifetime of ∼670 ns.
The XB<sub>n</sub><i>n</i> high operating temperature (HOT) detector project at SCD is aimed at developing a HOT (~150K) mid-wave
infrared (MWIR) detector array, based on InAsSb/AlSbAs barrier detector or "bariode" device elements. The essential
principle of the XB<sub>n</sub><i>n</i> bariode architecture is to suppress the Generation-Recombination contribution to the dark current
by ensuring that the depletion region of the device is contained inside a large bandgap <i>n</i>-type barrier layer (BL) and
excluded from the narrow bandgap <i>n</i>-type active layer (AL). The band profile of the XB<sub>n</sub><i>n</i> device leads to effective
blocking of electron transport across the BL while maintaining a free path for the holes, thus assuring a high internal
quantum efficiency (QE). Our devices exhibit a very large minority carrier lifetime (~700 ns), leading to a very low
dark current of <10<sup>-6</sup> A cm<sup>-2</sup> at 150K, which is essentially diffusion limited. We compare bariode devices with both a <i>p</i>-type
GaSb contact layer (CL) and an n-type InAsSb CL (termed C<sub>p</sub>B<sub>n</sub><i>n</i> and <i>n</i>B<sub>n</sub><i>n</i>, respectively). Apart from a ~0.3V
shift in the operating bias, the optical and electrical properties of both architectures are virtually identical,
demonstrating the generic nature of the XB<sub>n</sub><i>n</i> barrier detector family. We have fabricated FPAs from <i>n</i>B<sub>n</sub><i>n</i> bariode
arrays bonded both to a 320×256, 30 μm pitch Read-Out Integrated Circuit (ROIC) and a 640×512, 15 μm pitch ROIC.
For lattice matched FPAs the cut-off wavelength at >50% of maximum response is ~ 4.1 μm. We show an image
registered at 150K with a 640×512/15 μm Pelican FPA, using f/3.2 optics. The operability at 150K is >99.5% and the
measured NETD, limited only by shot and Read-Out noise, is 20 mK for a 22 ms integration time. At this f/number, the
detector has a background limited performance (BLIP) up to ~165K.
An XBn photovoltaic device has a band profile similar to that of a standard homojunction p-n diode, except that the
depletion region is made from a wide bandgap barrier material with a negligible valence band offset but a large
conduction band offset. In this notation, "X" stands for the n- or p-type contact layer, "B", for the n-type, wide bandgap,
barrier layer, and "n", for the n-type, narrow bandgap, active layer. In this work, we report on the fabrication of XBn
devices, which were grown by Molecular Beam Epitaxy (MBE) on GaSb substrates. Each structure has an InAsSb
active layer of thickness ~1.5μm and a 0.2-0.5μm thick AlSbAs barrier layer. Good growth uniformity was achieved
with lattice matching of better than 500ppm. Selected layers have been processed into devices which operate with a
high internal quantum efficiency at a bias of ~0.1-0.2V, and which exhibit a very low dark current due to the strong
suppression of the current component due to bulk Generation-Recombination processes. From dark current
measurements, a minority carrier lifetime of >670nS has been estimated in devices with an active layer doping of
~4×10<sup>15</sup>cm<sup>-3</sup>. In optimized, lattice matched, devices with this doping and an active layer thickness of 4μm, a cut-off
wavelength of ~ 4.0 - 4.1μm is expected at 160K, with a dark current density of ~10<sup>-6</sup> A cm<sup>-2</sup> and a quantum efficiency
of >70% (λ<4μm). These figures correspond to BLIP operation at 160K with a photocurrent to dark current ratio of ~4
Recently, a new "XB<i>n</i>" device architecture, based on heterostructures, has been proposed as an alternative to a
homojunction photodiode. The main difference is that no depletion layer exists in any narrow bandgap region of the
device. Instead, the depletion layer is confined to a wide bandgap barrier material. The Generation-Recombination (G-R)
contribution to the dark current is then almost totally suppressed and the dark current becomes diffusion limited.
This lowering of the dark current allows the device operating temperature to be raised relative to that of a standard
photodiode made from the same photon absorbing material, with essentially no loss of performance. At SCD we have
been developing XB<i>n</i> devices grown on GaSb substrates with an InAsSb photon absorbing layer and an AlSbAs barrier
layer. The results of optical and electrical measurements are presented on devices with a bandgap wavelength of about
4.1μm. Strong suppression of the G-R current is demonstrated over a range of almost two orders of magnitude in the
doping of the photon absorbing active layer (AL), while at the same time very high internal quantum efficiencies are
achieved. A model of the spectral response is developed which can reproduce the observed behaviour very well at 88K
and 150K over the whole AL doping range. In properly optimized devices, the BLIP temperature is shown to be in the
region of 160K at <i>f</i>/3.
Detectors composed of novel Antimonide Based Compound Semiconductor (ABCS) materials offer some unique
advantages. InAs/GaSb type II superlattices (T2SL) offer low dark currents and allow full bandgap tunability from the
MWIR to the VLWIR. InAs<sub>1-x</sub>Sb<sub>x</sub> alloys (x~0.1) also offer low dark currents and can be used to make MWIR devices
with a cut-off wavelength close to 4.2μm. Both can be grown on commercially available GaSb substrates and both can
be combined with lattice matched GaAlSbAs barrier layers to make a new type of High Operating Temperature (HOT)
detector, known as an XBn detector. In an XBn detector the Generation-Recombination (G-R) contribution to the dark
current can be suppressed, giving a lower net dark current, or allowing the same dark current to be reached at a higher
temperature than in a conventional photodiode. The ABCS program at SCD began several years ago with the
development of an epi-InSb detector whose dark current is about 15 times lower than in standard implanted devices.
This detector is now entering production. More recently we have begun developing infrared detectors based both on
T2SL and InAsSb alloy materials. Our conventional photodiodes made from T2SL materials with a cut-off wavelength
in the region of 4.6μm exhibit dark currents consistent with a BLIP temperature of ~ 120-130K at f/3. Characterization
results of the T2SL materials and diodes are presented. We have also initiated a program to validate the XBn concept
and to develop high operating temperature InAsSb XBn detectors. The crystallographic, electrical and optical properties
of the XBn materials and devices are discussed. We demonstrate a BLIP temperature of ~ 150K at f/3.